Integrated circuits often require voltage reference circuits. Reference circuits may be used to establish known voltage levels for controlling power supplies and other circuits. Ideally, reference circuits should exhibit good immunity to changes in process, voltage, and temperature (so-called PVT variations).
One popular type of reference circuit is the so-called bandgap reference circuit. Bandgap reference circuits exhibit stable behavior with respect to PVT variations, but are limited to producing output voltages at about 1.2 volts. Threshold-voltage-based complementary metal-oxide-semiconductor (CMOS) reference circuits have been developed that are capable of operating at lower output voltages, but this type of reference circuit tends to exhibit large amounts of process dependence, due to the dependence of threshold voltage on process (implant) variations.